U.S. patent application number 13/418136 was filed with the patent office on 2013-09-12 for systems and methods for temperature-controlled ablation using radiometric feedback in an interface module-based system.
The applicant listed for this patent is Eric R. Kanowsky, Timothy J. Lenhan, John McCarthy. Invention is credited to Eric R. Kanowsky, Timothy J. Lenhan, John McCarthy.
Application Number | 20130237977 13/418136 |
Document ID | / |
Family ID | 47997878 |
Filed Date | 2013-09-12 |
United States Patent
Application |
20130237977 |
Kind Code |
A1 |
McCarthy; John ; et
al. |
September 12, 2013 |
SYSTEMS AND METHODS FOR TEMPERATURE-CONTROLLED ABLATION USING
RADIOMETRIC FEEDBACK IN AN INTERFACE MODULE-BASED SYSTEM
Abstract
The present invention provides systems and methods for
temperature-controlled ablation using radiometric feedback. An
interface module may include (a) a processor; (b) a first
input/output (I/O) port to receive digital radiometer and digital
thermocouple signals from an integrated catheter tip (ICT); (c) a
second I/O port to receive ablative energy from a generator; (d) a
temperature display; (e) a patient relay; (f) a computer-readable
medium storing instructions for causing the processor to: (i)
calculate a temperature adjacent to the ICT based on the digital
radiometer and thermocouple signals and operation parameters; (ii)
cause the temperature display to display the calculated
temperature; and (iii) close the patient relay to pass ablative
energy received on the second I/O port to the first I/O port; and
(g) a temperature control subsystem to regulate the ablative power
based on the calculated temperature.
Inventors: |
McCarthy; John; (Newbury,
NH) ; Lenhan; Timothy J.; (Hradec Kralove, CZ)
; Kanowsky; Eric R.; (Santa Barbara, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
McCarthy; John
Lenhan; Timothy J.
Kanowsky; Eric R. |
Newbury
Hradec Kralove
Santa Barbara |
NH
CA |
US
CZ
US |
|
|
Family ID: |
47997878 |
Appl. No.: |
13/418136 |
Filed: |
March 12, 2012 |
Current U.S.
Class: |
606/20 ; 606/33;
606/41 |
Current CPC
Class: |
A61B 2018/00708
20130101; A61B 18/1206 20130101; A61B 18/082 20130101; A61B 18/1492
20130101; A61B 2017/00486 20130101; A61B 2018/00678 20130101; A61B
2017/0007 20130101; A61B 18/12 20130101; A61B 2018/00714 20130101;
A61B 2018/00642 20130101; A61B 2018/00577 20130101; A61B 18/02
20130101; A61N 7/022 20130101; A61B 18/1815 20130101; A61B
2018/00839 20130101; A61B 2218/002 20130101; A61N 7/02 20130101;
A61B 2018/00357 20130101; A61B 2018/00797 20130101; A61B 2018/00821
20130101 |
Class at
Publication: |
606/20 ; 606/41;
606/33 |
International
Class: |
A61B 18/14 20060101
A61B018/14; A61B 18/02 20060101 A61B018/02; A61B 18/18 20060101
A61B018/18 |
Claims
1. An interface module for use with an ablation energy generator
and an integrated catheter tip (ICT), the ICT including a
radiometer, an ablative tip, and a thermocouple, the interface
module comprising: a processor; a first input/output (I/O) port
configured to receive a digital radiometer signal and a digital
thermocouple signal from the ICT; a second I/O port configured to
receive ablative energy from the ablation energy generator; a
temperature display; a patient relay in communication with the
first I/O port, the second I/O port, and the processor; a
non-transitory computer-readable medium storing operation
parameters for the radiometer and for the thermocouple, and further
storing instructions for causing the processor to execute the steps
of: (a) calculating a temperature adjacent to the ICT based on the
digital radiometer signal, the digital thermocouple signal, and the
operation parameters; (b) causing the temperature display to
display the calculated temperature; and (c) closing the patient
relay such that the patient relay passes ablative energy received
on the second I/O port to the first I/O port; and a temperature
control subsystem configured to regulate the power of the ablative
energy based on the calculated temperature.
2. The interface module of claim 1, wherein the ablation energy
generator comprises a power control, and wherein the temperature
control subsystem comprises: a processor; a power control interface
configured to be operatively coupled to the power control of the
ablation energy generator; and a memory storing a setpoint and
instructions for causing the processor to execute the steps of: (a)
comparing the calculated temperature to the setpoint, (b) if the
calculated temperature is below the setpoint, increasing the
ablation energy power with the power control interface; and (c) if
the calculated temperature is above the setpoint, reducing the
ablation energy power with the power control interface.
3. The interface module of claim 2, wherein the power control of
the ablation energy generator comprises a knob, and wherein the
power control interface comprises a stepper motor configured to
mechanically turn the knob.
4. The interface module of claim 2, wherein the power control
interface is configured to allow a clinician to manually adjust the
ablation energy power.
5. The interface module of claim 1, further comprising a load relay
and a dummy load, and wherein the computer-readable medium further
stores a safety cutoff temperature and instructions for causing the
processor to execute the steps of: (d) comparing the calculated
temperature to the safety cutoff temperature while the patient
relay is closed; and (e) if the calculated temperature exceeds the
safety cutoff temperature, opening the patient relay and closing
the load relay such that the load relay passes ablative energy
received on the second I/O port to the dummy load.
6. The interface module of claim 1, wherein the instructions cause
the processor to maintain the patient relay in a normally closed
state and to open the patient relay upon detection of an unsafe
condition.
7. The interface module of claim 1, wherein the computer-readable
medium further stores instructions for causing the processor to
execute the steps of: (d) initially calculating a temperature
adjacent to the ICT based on the digital thermocouple and the
operation parameters but not the digital radiometer signal; (e)
causing the temperature display to display the initially calculated
temperature; and (f) if the temperature calculated in step (d) is
in the range of 35.degree. C. to 39.degree. C. and if the second
I/O port is receiving ablative energy from the ablation energy
generator, then executing steps (a)-(c).
8. The interface module of claim 1, further comprising a third I/O
port configured to receive a signal from an indifferent electrode
and a fourth I/O port configured to provide the signal from the
indifferent electrode to the ablation energy generator.
9. The interface module of claim 1, wherein the ablative energy is
selected from the group consisting of RF energy, microwave energy,
cryoablation energy, and high frequency ultrasound energy.
10. The interface module of claim 1, wherein the ablative energy is
RF energy.
11. A method of using an interface module with an ablation energy
generator and an integrated catheter tip (ICT), the ICT including a
radiometer, an ablative tip, and a thermocouple, the method of
using the interface module comprising the steps of: (a) receiving
at a first I/O port of the interface module a digital radiometer
signal and a digital thermocouple signal from the ICT; (b)
receiving at a second I/O port of the interface module ablative
energy from the ablation energy generator; (c) calculating at the
interface module a temperature adjacent to the ICT based on the
digital radiometer signal, the digital thermocouple signal, and the
operation parameters; (d) displaying on a temperature display of
the interface module the calculated temperature; (e) passing
ablative energy received on the second I/O port to the first I/O
port by closing a patient relay of the ablation module; and (f)
automatically regulating the power of the ablative energy based on
the calculated temperature.
12. The method of claim 11, wherein the ablation energy generator
comprises a power control, the method further comprising the steps
of: (g) operatively coupling a power control interface to the power
control of the ablation energy generator; (h) storing a setpoint;
(i) comparing the calculated temperature to the setpoint; (j) if
the calculated temperature is below the setpoint, increasing the
ablation energy power with the power control interface; and (k) if
the calculated temperature is above the setpoint, reducing the
ablation energy power with the power control interface.
13. The method of claim 12, wherein the power control of the
ablation energy generator comprises a knob, wherein the power
control interface comprises a stepper motor, and wherein steps (j)
and (k) comprise mechanically turning the knob with a stepper
motor.
14. The method of claim 12, wherein the power control interface is
configured to allow a clinician to manually adjust the ablation
energy power.
15. The method of claim 11, further comprising the steps of: (g)
storing at the interface module a safety cutoff temperature; (h) at
the interface module, comparing the calculated temperature to the
safety cutoff temperature while the patient relay is closed; and
(i) if the calculated temperature exceeds the safety cutoff
temperature, opening the patient relay and closing a load relay of
the ablation module such that the load relay passes ablative energy
received on the second I/O port to a dummy load of the ablation
module.
16. The method of claim 11, wherein the patient relay is maintained
in a normally closed state and opened upon detection of an unsafe
condition.
17. The method of claim 11, further comprising the steps of: (g)
initially calculating at the interface module a temperature
adjacent to the ICT based on the digital thermocouple and the
operation parameters but not the digital radiometer signal; (h)
displaying on the temperature display the initially calculated
temperature; and (i) if the temperature calculated in step (f) is
in the range of 35.degree. C. to 39.degree. C. and if the second
I/O port is receiving ablative energy from the ablation energy
generator, then performing steps (c)-(e).
18. The method of claim 11, further comprising the steps of: (f)
receiving at a third I/O port of the ablation energy generator a
signal from an indifferent electrode; and (g) providing at a fourth
I/O port the signal from the indifferent electrode to the ablation
energy generator.
19. The method of claim 11, wherein the ablative energy is selected
from the group consisting of RF energy, microwave energy,
cryoablation energy, and high frequency ultrasound energy.
20. The method of claim 11, wherein the ablative energy is RF
energy.
Description
FIELD OF THE INVENTION
[0001] This application generally relates to systems and methods
for measuring and controlling temperature during tissue
ablation.
BACKGROUND OF THE INVENTION
[0002] Tissue ablation may be used to treat a variety of clinical
disorders. For example, tissue ablation may be used to treat
cardiac arrhythmias by destroying aberrant pathways that would
otherwise conduct abnormal electrical signals to the heart muscle.
Several ablation techniques have been developed, including
cryoablation, microwave ablation, radio frequency (RF) ablation,
and high frequency ultrasound ablation. For cardiac applications,
such techniques are typically performed by a clinician who
introduces a catheter having an ablative tip to the endocardium via
the venous vasculature, positions the ablative tip adjacent to what
the clinician believes to be an appropriate region of the
endocardium based on tactile feedback, mapping electrocardiogram
(ECG) signals, anatomy, and/or fluoroscopic imaging, actuates flow
of an irrigant to cool the surface of the selected region, and then
actuates the ablative tip for a period of time and at a power
believed sufficient to destroy tissue in the selected region.
[0003] Although commercially available ablative tips may include
thermocouples for providing temperature feedback via a digital
display, such thermocouples typically do not provide meaningful
temperature feedback during irrigated ablation. For example, the
thermocouple only measures surface temperature, whereas the heating
or cooling of the tissue that results in tissue ablation may occur
at some depth below the tissue surface. Moreover, for procedures in
which the surface of the tissue is cooled with an irrigant, the
thermocouple will measure the temperature of the irrigant, thus
further obscuring any useful information about the temperature of
the tissue, particularly at depth. As such, the clinician has no
useful feedback regarding the temperature of the tissue as it is
being ablated or whether the time period of the ablation is
sufficient. Because the clinician lacks such information, the
clinician furthermore cannot regulate the power of the ablation
energy so as to heat or cool the tissue to the desired temperature
for a sufficient period of time.
[0004] Accordingly, it may only be revealed after the procedure is
completed--for example, if the patient continues to experience
cardiac arrhythmias--that the targeted aberrant pathway was not
adequately interrupted. In such a circumstance, the clinician may
not know whether the procedure failed because the incorrect region
of tissue was ablated, because the ablative tip was not actuated
for a sufficient period of time to destroy the aberrant pathway,
because the ablative tip was not touching or sufficiently touching
the tissue, because the power of the ablative energy was
insufficient, or some combination of the above. Upon repeating the
ablation procedure so as to again attempt to treat the arrhythmia,
the clinician may have as little feedback as during the first
procedure, and thus potentially may again fail to destroy the
aberrant pathway. Additionally, there may be some risk that the
clinician would re-treat a previously ablated region of the
endocardium and not only ablate the conduction pathway, but damage
adjacent tissues.
[0005] In some circumstances, to avoid having to repeat the
ablation procedure as such, the clinician may ablate a series of
regions of the endocardium along which the aberrant pathway is
believed to lie, so as to improve the chance of interrupting
conduction along that pathway. However, there is again insufficient
feedback to assist the clinician in determining whether any of
those ablated regions are sufficiently destroyed.
[0006] U.S. Pat. No. 4,190,053 to Sterzer describes a hyperthermia
treatment apparatus in which a microwave source is used to deposit
energy in living tissue to effect hyperthermia. The apparatus
includes a radiometer for measuring temperature at depth within the
tissue, and includes a controller that feeds back a control signal
from the radiometer, corresponding to the measured temperature, to
control the application of energy from the microwave source. The
apparatus alternates between delivering microwave energy from the
microwave source and measuring the radiant energy with the
radiometer to measure the temperature. As a consequence of this
time division multiplexing of energy application and temperature
measurement, temperature values reported by the radiometer are not
simultaneous with energy delivery.
[0007] U.S. Pat. No. 7,769,469 to Carr et al. describes an
integrated heating and sensing catheter apparatus for treating
arrhythmias, tumors and the like, having a diplexer that permits
simultaneous heating and temperature measurement. This patent too
describes that temperature measured by the radiometer may be used
to control the application of energy, e.g., to maintain a selected
heating profile.
[0008] Despite the promise of precise temperature measurement
sensitivity and control offered by the use of radiometry, there
have been few successful commercial medical applications of this
technology. One drawback of previously-known systems has been an
inability to obtain highly reproducible results due to slight
variations in the construction of the microwave antenna used in the
radiometer, which can lead to significant differences in measured
temperature from one catheter to another. Problems also have arisen
with respect to orienting the radiometer antenna on the catheter to
adequately capture the radiant energy emitted by the tissue, and
with respect to shielding high frequency microwave components in
the surgical environment so as to prevent interference between the
radiometer components and other devices in the surgical field.
[0009] Acceptance of microwave-based hyperthermia treatments and
temperature measurement techniques also has been impeded by the
capital costs associated with implementing radiometric temperature
control schemes. Radiofrequency ablation techniques have developed
a substantial following in the medical community, even though such
systems can have severe limitations, such as the inability to
accurately measure tissue temperature at depth, e.g., where
irrigation is employed. However, the widespread acceptance of RF
ablation systems, extensive knowledge base of the medical community
with such systems, and the significant cost required to changeover
to, and train for, newer technologies has dramatically retarded the
widespread adoption of radiometry.
[0010] In view of the foregoing, it would be desirable to provide
apparatus and methods that permit radiometric measurement of
temperature at depth in tissue, and permit use of such measurements
to control the application of ablation energy in an ablation
treatment, e.g., a hyperthermia or hypothermia treatment,
particularly in an automated fashion so as to maintain a target
region of tissue at a desired temperature for a desired period of
time.
[0011] It further would be desirable to provide apparatus and
methods that employ microwave radiometer components that can be
readily constructed and calibrated to provide a high degree of
measurement reproducibility and reliability.
[0012] It also would be desirable to provide apparatus and methods
that permit radiometric temperature measurement and control
techniques to be introduced in a manner that is readily accessible
to clinicians trained in the use of previously-known RF ablation
catheters, with a minimum of retraining.
[0013] It still further would be desirable to provide apparatus and
methods that permit radiometric temperature measurement and control
techniques to be readily employed with previously-known RF
electrosurgical generators, thereby reducing the capital costs
needed to implement such new techniques.
SUMMARY OF THE INVENTION
[0014] In view of the foregoing, it would be desirable to provide
apparatus and methods for treating living tissue that employs a
radiometer for temperature measurement, and a temperature control
subsystem that uses feedback from the radiometer to regulate the
power of ablation energy being applied to the tissue. In accordance
with one aspect of the invention, systems and methods are provided
for radiometrically measuring temperature during RF ablation, i.e.,
calculating temperature based on signal(s) from a radiometer.
Unlike standard thermocouple techniques used in existing commercial
ablation systems, a radiometer may provide useful information about
tissue temperature at depth--where the tissue ablation occurs--and
thus provide feedback to the clinician about the extent of tissue
damage as the clinician ablates a selected region of the heart
muscle. Furthermore, the temperature control subsystem may
automatically regulate the power of the ablation energy applied to
the tissue based on the tissue temperature, so as to maintain the
tissue at the desired temperature and for the desired amount of
time to achieve sufficient ablation.
[0015] In one embodiment, the present invention comprises an
interface module (system) that may be coupled to a previously-known
commercially available ablation energy generator, e.g., an
electrosurgical generator, thereby enabling radiometric techniques
to be employed with reduced capital outlay. In this manner, the
conventional electrosurgical generator can be used to supply
ablative energy to an "integrated catheter tip" (ICT) that includes
an ablative tip, a thermocouple, and a radiometer for detecting the
volumetric temperature of tissue subjected to ablation. The
interface module is configured to be coupled between the
conventional electrosurgical generator and the ICT, and to
coordinate signals therebetween. The interface module thereby
provides the electrosurgical generator with the information
required for operation, transmits ablative energy to the ICT under
the control of the clinician, and displays via a temperature
display the temperature at depth of tissue as it is being ablated,
for use by the clinician. The displayed temperature may be
calculated based on signal(s) measured by the radiometer using
algorithms such as discussed further below. The interface module
further includes a temperature control subsystem configured to
interface with the power control of the electrosurgical generator.
The temperature control subsystem stores a setpoint temperature to
which the tissue is to be heated, and regulates the power control
of the electrosurgical generator based on the setpoint temperature
and on the calculated temperature of the tissue so as to bring the
calculated tissue temperature to the setpoint temperature and
maintain it at that value for a desired period of time.
[0016] In an exemplary embodiment, the interface module includes a
first input/output (I/O) port that is configured to receive a
digital radiometer signal and a digital thermocouple signal from
the ICT, and a second I/O port that is configured to receive
ablative energy from the electrosurgical generator. The interface
module also includes a processor, a patient relay in communication
with the processor and the first and second I/O ports, and a
persistent computer-readable medium. The computer-readable medium
stores operation parameters for the radiometer and the
thermocouple, as well as instructions for the processor to use in
coordinating operation of the ICT and the electrosurgical
generator.
[0017] The computer-readable medium preferably stores instructions
that cause the processor to execute the step of calculating a
temperature adjacent to the ICT based on the digital radiometer
signal, the digital thermocouple signal, and the operation
parameters. This temperature is expected to provide significantly
more accurate information about lesion quality and temperature at
depth in the tissue than would a temperature based solely on a
thermocouple readout. The computer-readable medium may further
store instructions for causing the processor to cause the
temperature display to display the calculated temperature, for
example so that the clinician may control the time period for
ablation responsive to the displayed temperature. The
computer-readable medium may further store instructions for causing
the processor to close the patient relay, such that the patient
relay passes ablative energy received on the second I/O port, from
the electrosurgical generator, to the first I/O port, to the ICT.
Note that the instructions may cause the processor to maintain the
patient relay in a normally closed state, and to open the patient
relay upon detection of unsafe conditions.
[0018] The interface module further includes a temperature control
subsystem that regulates the power of the ablative energy based on
the calculated temperature.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1A is a schematic illustration of a first embodiment of
an arrangement including an interface module, temperature control
subsystem, and power control interface according to one aspect of
the present invention, including a display of the front and back
panels of, and exemplary connections between, the interface module,
temperature control subsystem, power control interface, a
previously known ablation energy generator, e.g., electrosurgical
generator, and an integrated catheter tip (ICT).
[0020] FIG. 1B is a schematic illustrating exemplary connections to
and from the interface module, temperature control subsystem, and
power control interface of FIG. 1A, as well as connections among
other components that may be used with the same.
[0021] FIG. 1C is a schematic illustrating exemplary connections to
and from an alternative embodiment of an interface module,
temperature control subsystem, and power control interface, as well
as connections among other components that may be used with the
same.
[0022] FIG. 1D is a schematic illustrating exemplary connections to
and from another alternative embodiment of an interface module,
temperature control subsystem, and power control interface, as well
as connections among other components that may be used with the
same.
[0023] FIG. 1E is a schematic illustrating exemplary connections to
and from yet another alternative embodiment of an interface module,
temperature control subsystem, and power control interface, as well
as connections among other components that may be used with the
same.
[0024] FIG. 2A is a schematic illustrating internal components of
the interface module of FIG. 1A-1B.
[0025] FIG. 2B schematically illustrates additional internal
components of the interface module of FIG. 2A, as well as selected
connections to and from the interface module.
[0026] FIG. 2C is a schematic illustrating internal components of
the temperature control subsystem of FIGS. 1A-1B.
[0027] FIG. 2D illustrates a perspective view of an exemplary
temperature control subsystem, power control interface, and
interface module coupled to each other and to a previously-known
ablation energy generator in accordance with the embodiment
illustrated in FIGS. 1A-1B and 2A-2C.
[0028] FIG. 3A illustrates steps in a method of using the interface
module and temperature control subsystem of FIGS. 1A-2D during
tissue ablation.
[0029] FIG. 3B illustrates steps in a method of calculating
radiometric temperature using digital signals from a radiometer and
a thermocouple and operation parameters.
[0030] FIG. 3C illustrates steps in a method of controlling an
ablation procedure using a temperature calculated based on
signal(s) from a radiometer using the interface module and
temperature control subsystem of FIGS. 1A-2D.
[0031] FIGS. 4A-4F illustrate data obtained during exemplary
ablation procedures performed using the interface module,
temperature control subsystem, and power control interface of FIGS.
1A-1B and 2A-2D operated in accordance with the methods of FIGS.
3A-3C.
[0032] FIG. 5A illustrates a plan view of an exemplary patient
interface module (PIM) associated with an integrated catheter tip
(ICT) for use with the interface module, temperature control
subsystem, and power control interface of FIGS. 1A-2D.
[0033] FIG. 5B schematically illustrates selected internal
components of the PIM of FIG. 5A, according to some embodiments of
the present invention.
[0034] FIGS. 6A-6B respectively illustrate perspective and exploded
views of an exemplary integrated catheter tip (ICT) for use with
the interface module, temperature control subsystem, and power
control interface of FIGS. 1A-2D and the PIM of FIGS. 5A-5B,
according to some embodiments of the present invention.
DETAILED DESCRIPTION
[0035] Embodiments of the present invention provide systems and
methods for radiometrically measuring temperature during ablation,
in particular cardiac ablation, and for automatically regulating
the power of ablation energy based on same. As noted above,
commercially available systems for cardiac ablation may include
thermocouples for measuring temperature, but such thermocouples may
not adequately provide the clinician with information about tissue
temperature. Thus, the clinician may need to make an "educated
guess" about whether a given region of tissue has been sufficiently
ablated to achieve the desired effect. By comparison, calculating a
temperature based on signal(s) from a radiometer is expected to
provide accurate information to the clinician about the temperature
of tissue at depth, even during an irrigated procedure.
Furthermore, a temperature control subsystem may be employed that
monitors the calculated temperature, and automatically regulates or
controls the power of ablation energy provided to the tissue so as
to maintain the tissue at a desired temperature and for a desired
time to achieve sufficient ablation. The present invention provides
a "retrofit" solution that includes an interface module that works
with existing, commercially available ablation energy generators,
such as electrosurgical generators. In accordance with one aspect
of the present invention, the interface module displays a tissue
temperature based on signal(s) measured by a radiometer and
includes, or is connected to, a temperature control subsystem that
controls or regulates the power of ablation energy based on same
via a power control interface, such that a clinician may perform
ablation procedures with significantly better accuracy than can be
achieved using only a thermocouple for temperature measurement.
[0036] First, high level overviews of the interface module,
including the connected or integrated temperature control subsystem
and power control interface, and connections thereto are provided.
Then, further detail on the internal components of the interface
module, temperature control subsystem, and power control interface,
alternative embodiments thereof, and exemplary methods of
calculating radiometric temperature and controlling an ablation
procedure using the same, are provided. Data obtained during
experimental procedures also is presented. Lastly, further detail
on components that may be used with the interface module,
temperature control subsystem, and power control interface is
provided.
[0037] FIG. 1A illustrates plan views of exemplary interface module
110, temperature control subsystem 119, and power control
interface, which are constructed in accordance with the principles
of the present invention. As described in greater detail below,
temperature control subsystem 119 is in communication with the
power control functionality of electrosurgical generator 130, and
is configured to control the power of ablation energy generated by
generator 130 responsive to the temperature calculated by interface
module 110, by sending appropriate control signals to power control
interface 290 that adjusts the power generated by generator 130.
Temperature control subsystem 119, power control interface 290, and
interface module 110 may be separate from one another and connected
by appropriate cabling as illustrated in FIGS. 1A-1B, or
alternatively may be integrated into one or more modules having
combined functionality, as described in greater detail below with
reference to FIGS. 1C-1E.
[0038] As illustrated in FIG. 1A, front panel 111 of interface
module 110 may be connected to a catheter 120 that includes patient
interface module (PIM) 121 and integrated catheter tip (ICT) 122.
Catheter 120 optionally is steerable, or may be non-steerable and
used in conjunction with a robotic positioning system or a
third-party steerable sheath (not shown). ICT 122 is positioned by
a clinician (optionally with mechanical assistance such as noted
above), during a procedure, within subject 101 lying on grounded
table 102. ICT 122 may include, among other things, an ablative
tip, a thermocouple, and a radiometer for detecting the volumetric
temperature of tissue subjected to ablation. The ICT 122 optionally
includes one or more irrigation ports, which in one embodiment may
be connected directly to a commercially available irrigant
pump.
[0039] In embodiments in which the ablation energy is
radiofrequency (RF) energy, the ablative tip may include an
irrigated ablation electrode, such as described in greater detail
below with reference to FIGS. 6A-6B. ICT 122 further may include
one or more electrocardiogram (ECG) electrodes for use in
monitoring electrical activity of the heart of subject 101.
Interface module 110 receives signals from the thermocouple,
radiometer, and optional ECG electrodes of ICT 122 via PIM 121.
Interface module 110 provides to ICT 122, via PIM 121, power for
the operation of the PIM and the sensors (thermocouple, radiometer,
and ECG electrodes), and ablation energy to be applied to subject
101 via the ablative tip.
[0040] Back panel 112 of interface module 110 may be connected via
connection cable 135 to a commercially available previously-known
ablation energy generator 130, for example an electrosurgical
generator 130, such as a Stockert EP-Shuttle 100 Generator
(Stockert GmbH, Freiburg Germany) or Stockert 70 RF Generator
(Biosense Webster, Diamond Bar, Calif.). In embodiments where the
electrosurgical generator 130 is a Stockert EP-Shuttle or 70 RF
Generator, generator 130 includes display device 131 for displaying
temperature and the impedance and time associated with application
of a dose of RF ablation energy; power control knob 132 for
allowing a clinician to manually adjust the power of RF ablative
energy delivered to subject 101; and start/stop/mode input 133 for
allowing a clinician to initiate or terminate the delivery of RF
ablation energy. Start/stop/mode input 133 also may be configured
to control the mode of energy delivery, e.g., whether the energy is
to be cut off after a given period of time.
[0041] Although generator 130 may be configured to display
temperature on display device 131, that temperature is based on
readings from a standard thermocouple. As noted above, however,
that reported temperature may be inaccurate while irrigant and
ablative energy are being applied to tissue. Interface module 110
provides to generator 130, via connection cable 135, a thermocouple
signal for use in displaying such a temperature, and signals from
the ECG electrodes; and provides via indifferent electrode cable
134 a pass-through connection to indifferent electrode 140.
Interface module 110 receives from generator 130, via connection
cable 135, RF ablation energy that module 110 controllably provides
to ICT 122 for use in ablating tissue of subject 101.
[0042] As noted above, temperature control subsystem 119 is
configured to control the power of ablation energy provided to ICT
122. In the illustrated embodiment, temperature control subsystem
119 is coupled to interface module 110 via temperature control
cable 136, or alternatively may be an internal component of
interface module 110 as described below with reference to FIG. 1D.
Temperature control subsystem 119 is coupled to power control
interface 290 which is operatively coupled to the power control of
generator 130, e.g., is mechanically coupled to power control knob
132, and is configured to regulate ablation power based on the
tissue temperature calculated by interface module 110, for example
using a stepper motor 291 as described below with reference to FIG.
2D. In the illustrated embodiment, power control interface 290 is
coupled to temperature control subsystem 119 via power control
cable 137. However, it should be understood that temperature
control subsystem 119 and power control interface 290 may be
integrated into a single unit, i.e., disposed within a single
housing, such as described below with reference to FIG. 1C.
Moreover, it should further be understood that temperature control
subsystem 119, power control interface, and interface module 110
may be integrated into a single unit, i.e., disposed within a
single housing, for example as illustrated below with reference to
FIG. 1E.
[0043] In the embodiment illustrated in FIG. 1A, back panel 112 of
interface module 110 includes data ports 114 that are configured to
output one or more signals to temperature control subsystem 119,
via control cable 136, for use in automatically regulating the
power of ablation energy generated by electrosurgical generator
130. Such signals may include, for example, the tissue temperature
calculated by interface module 110, and the power of ablation
energy that interface module 110 receives from generator 130. As
described in greater detail below, temperature control subsystem
119 stores a target temperature (setpoint) to which the tissue
temperature is to be raised, and also includes a processor that
calculates a power at which the ablation energy is to be provided
to ICT 122 through interface module 110. The temperature control
subsystem 119 sends control signals to power control interface 290,
via cable 137, that cause the power control interface to
mechanically manipulate the power control knob 132 of generator 130
such that the ablation energy is provided at this power. Other
methods of controlling the power of ablation energy of generator
130 also may be used, for example by instead transmitting an
appropriate control signal to generator 130 to cause generator 130
to output ablation energy at a desired power. In either embodiment,
the coupling between temperature control subsystem 119, power
control interface 290, and generator 130 preferably is configured
such that a clinician may manually override the automated power
control at any time during an ablation procedure.
[0044] As will be familiar to those skilled in the art, for a
monopolar RF ablation procedure, a clinician may position an
indifferent electrode (IE) 140 on the back of subject 101 so as to
provide a voltage differential that enables transmission of RF
energy into the tissue of the subject. In the illustrated
embodiment, IE 140 is connected to interface module 110 via first
indifferent electrode cable 141. Interface module 110 passes
through the IE signal to second indifferent electrode cable 134,
which is connected to an indifferent electrode input port on
electrosurgical generator 130. Alternatively, the IE may be
connected directly to that port of the electrosurgical generator
130 via appropriate cabling (not shown).
[0045] It should be understood that electrosurgical generators
other than the Stockert EP-Shuttle or 70 RF Generator suitably may
be used, e.g., other makes or models of RF electrosurgical
generators. Alternatively, generators that produce other types of
ablation energy, such as microwave generators, cryosurgical
sources, or high frequency ultrasound generators, may be used, and
the power of ablation energy generated by such generators may be
suitably regulated using an appropriate mechanism (e.g., by
mechanically adjusting a control knob via control interface 290 or
by providing a control signal via appropriate cabling). Ablation
energy generator 130 need not necessarily be commercially
available, although as noted above it may be convenient to use one
that is. It should also be appreciated that the connections
described herein may be provided on any desired face or panel of
interface module 110, and that the functionalities of different
connectors and input/output (I/O) ports may be combined or
otherwise suitably modified.
[0046] Front panel 111 of interface module 110 includes temperature
display 113, e.g., a digital two or three-digit display device
configured to display a temperature calculated by a processor
internal to interface module 110, e.g., as described in greater
detail below with reference to FIGS. 2A-2B and 3A. Other types of
temperature displays, such multicolor liquid crystal displays
(LCDs), alternatively may be used. Front panel 111 also includes
connectors (not labeled) through which interface module 110 is
connected to ICT 122 via PIM 121, and to the IE 140 via indifferent
electrode cable 141.
[0047] Back panel 112 of interface module 110 includes connectors
(not labeled) through which interface module 110 is connected to
electrosurgical generator 130, via indifferent electrode cable 134
and connection cable 135. The data ports 114 of interface module
110, which as noted above provide information to temperature
control subsystem 119, also may be configured to output one or more
signals to a suitably programmed personal computer or other remote
device, for example an EP monitoring/recording system such as the
LABSYSTEM.TM. PRO EP Recording System (C.R. Bard, Inc., Lowell,
Mass.). Such signals may, for example, include signals generated by
the thermocouple, radiometer, and/or ECG electrodes of the ICT, the
tissue temperature calculated by interface module 110, the power of
ablation energy being provided to ICT 122, and the like.
[0048] Referring now to FIG. 1B, exemplary connections to and from
interface module 110, externally coupled temperature control
subsystem 119, and externally coupled power control interface 290
of FIG. 1A, as well as connections among other components, are
described. Examples of alternative configurations for partially or
fully integrated combinations of interface module 110, temperature
control subsystem 119, and power control interface are described
below with reference to FIGS. 1C-1E.
[0049] In FIG. 1B, interface module 110 is in operable
communication with catheter 120 having an integrated catheter tip
(ICT) 122 that includes a radiometer, ablative tip, a thermocouple
(TC), and optionally also includes ECG electrodes and/or irrigation
ports(s), via patient interface module (PIM) 121. Interface module
110 is in operable communication with temperature control subsystem
119 via temperature control cable 136, is in operable communication
with electrosurgical generator 130 via connection cable 135, and is
in operable communication with indifferent electrode 140 via
indifferent electrode cable 141, such as discussed above with
reference to FIG. 1A. Temperature control subsystem 119 is in
operable communication with power control interface 290 via power
control cable 137. Power control interface 290 is in operable
communication with power control 132 of ablation energy generator
130 via stepper motor 291 described further below with reference to
FIG. 2D.
[0050] As illustrated in FIG. 1B, electrosurgical generator 130
optionally is in operable communication with electrophysiology (EP)
monitoring/recording system 160 via appropriate cabling 161, or
alternatively via data ports 114 of interface module 110 and
appropriate cabling. EP monitoring/recording system 160 may
include, for example, various monitors, processors, and the like
that display pertinent information about an ablation procedure to a
clinician, such as the subject's heart rate and blood pressure, the
temperature recorded by the thermocouple on the catheter tip, the
ablation power and time period over which it is applied,
fluoroscopic images, and the like. EP monitoring/recording systems
are commercially available, e.g., the MEDELEC.TM. Synergy
T-EP-EMG/EP Monitoring System (CareFusion, San Diego, Calif.), or
the LABSYSTEM.TM. PRO EP Recording System (C.R. Bard, Inc., Lowell,
Mass.).
[0051] If the ICT 122 includes irrigation port(s), then one
convenient means of providing irrigant to such ports is irrigation
pump 140 associated with electrosurgical generator 130, which pump
is in operable communication with the generator and in fluidic
communication with the ICT via connector 151. For example, the
Stockert 70 RF Generator is designed for use with a CoolFlow.TM.
Irrigation pump, also manufactured by Biosense Webster.
Specifically, the Stockert 70 RF Generator and the CoolFlow.TM.
pump may be connected to one another by a commercially available
interface cable, so as to operate as an integrated system that
works in substantially the same way as it would with a standard,
commercially available catheter tip. For example, prior to
positioning ICT 122 in the body, the clinician instructs the pump
to provide a low flow rate of irrigant to the ICT, as it would to a
standard catheter tip; the ICT is then positioned in the body.
Then, when the clinician presses the "start" button on the face of
generator 130, the generator may instruct pump 150 to provide a
high flow rate of irrigant for a predetermined period (e.g., 5
seconds) before providing RF ablation energy, again as it would for
a standard catheter tip. After the RF ablation energy application
is terminated, then pump 150 returns to a low flow rate until the
clinician removes the ICT 122 from the body and manually turns off
the pump.
[0052] As noted above, the functionalities of interface module 110,
temperature control subsystem 119, and/or power control interface
290 optionally may be integrated with one another. For example,
FIG. 1C illustrates an embodiment in which alternative temperature
control subsystem 119c and alternative power control interface 290c
are integrated with one another, e.g., located within the same
housing with one another. Integrated temperature control
subsystem/power control interface 119c, 290c may be connected to
interface module 110 via temperature control cable 136, and may be
connected to power control 132 of ablation energy generator 130 via
stepper motor 291 described further below with reference to FIG.
2D. Other connections may be substantially the same as described
above with reference to FIGS. 1A-1B.
[0053] Or, for example, FIG. 1D illustrates an embodiment in which
interface module 110d and alternative temperature control subsystem
119d are integrated with one another, e.g., located within the same
housing with one another. Integrated interface module/temperature
control subsystem 110d/119d may be connected to catheter 120 via
PIM 121, may be connected to ablation energy generator 130 via
connection cable 135, and may be connected to power control 132 of
ablation energy generator 130 via power control cable 137, power
control interface 290, and stepper motor 291. Other connections may
be substantially the same as described above with reference to
FIGS. 1A-1B.
[0054] As still another example, FIG. 1E illustrates an embodiment
in which alternative interface module 110e, alternative temperature
control subsystem 119e, and alternative power control interface
290e are integrated with one another, e.g., located within the same
housing with one another. Integrated interface module/temperature
control subsystem/power control interface 110e, 119e, 290e may be
connected to ablation energy generator 130 via connection cable
135, and may be connected to power control 132 of ablation energy
generator 130 via stepper motor 291. Other connections may be
substantially the same as described above with reference to FIGS.
1A-1B
[0055] Referring now to FIGS. 2A-2D, further details of internal
components of interface module 110, temperature control subsystem
119, and power control interface 290 of FIGS. 1A-1B are provided.
It should be understood that such components suitably may be
modified to alternatively configure module 110, subsystem 119, and
interface 290 in partially or fully integrated modules such as
shown in FIGS. 1C-1E.
[0056] FIG. 2A schematically illustrates internal components of one
embodiment of interface module 110. Interface module 110 includes
first, second, third, and fourth ports 201-204 by which it
communicates with external components. Specifically, first port 201
is an input/output (I/O) port configured to be connected to
catheter 120 via PIM 121, as illustrated in FIG. 1A. Port 201
receives as input from catheter 120 digital radiometer and digital
thermocouple (TC) signals, and optionally ECG signals, generated by
ICT 122, and provides as output to catheter 120 RF ablation energy,
as well as power for circuitry within the ICT 122 and the PIM 121.
Second port 202 is also an I/O port, configured to be connected to
electrosurgical generator 130 via connection cable 135 illustrated
in FIG. 1A, and receives as input from generator 130 RF ablation
energy, and provides as output to generator 130 a reconstituted
analog thermocouple (TC) signal and raw ECG signal(s). Third port
203 is an input port configured to be connected to indifferent
electrode (IE) 140 via indifferent electrode cable 134 illustrated
in FIG. 1A, and fourth port 204 is an output port configured to be
connected to generator 130 via indifferent electrode cable 141
illustrated in FIG. 1A. As shown in FIG. 2A, interface module 110
acts as a pass-through for the IE signal from IE 140 to generator
130, and simply receives IE signal on third port 203 and provides
the IE signal to generator 130 on fourth port 204.
[0057] Interface module 110 also includes processor 210 coupled to
non-volatile (persistent) computer-readable memory 230, user
interface 280, load relay 260, and patient relay 250. Memory 230
stores programming that causes processor 210 to perform steps
described further below with respect to FIGS. 3A-3C, thereby
controlling the functionality of interface module 110. Memory 230
also stores parameters used by processor 210. For example, memory
230 may store a set of operation parameters 231 for the
thermocouple and radiometer, as well as a temperature calculation
module 233, that processor 210 uses to calculate the radiometric
temperature based on the digital TC and radiometer signals received
on first I/O port 201, as described in greater detail below with
respect to FIG. 3B. The operation parameters 231 may be obtained
through calibration, or may be fixed. Memory 230 also stores a set
of safety parameters 232 that processor 210 uses to maintain safe
conditions during an ablation procedure, as described further below
with respect to FIG. 3C. Memory 230 further stores decision module
234 that processor 210 uses to control the opening and closing of
patient relay 250 and load relay 260 based on its determinations of
temperature and safety conditions, as described further below with
reference to FIGS. 3A-3C. When closed, patient relay 250 passes
ablative energy from the second I/O port 202 to the first I/O port
201. When closed, load relay 260 returns ablative energy to the IE
140 via dummy load D (resistor, e.g., of 120 .OMEGA.resistance) and
fourth I/O port 204.
[0058] As illustrated in FIG. 2A, interface module 110 further
includes user interface 280 by which a user may receive information
about the temperature adjacent ICT 122 as calculated by processor
210, as well as other potentially useful information. In the
illustrated embodiment, user interface 280 includes digital
temperature display 113, which displays the instantaneous
temperature calculated by processor 210. In other embodiments (not
shown), display 113 may be an LCD device that, in addition to
displaying the instantaneous temperature calculated by processor
210, also graphically display changes in the temperature over time
for use by the clinician during the ablation procedure. User
interface 280 further includes data ports 114, one or more of which
are connected to temperature control subsystem 119 to provide the
calculated temperature and/or ablation energy power to subsystem
119. Data ports 114 also optionally may be connected to a computer
or EP monitoring/recording system 160 by appropriate cabling 161 as
noted above, and which may output digital or analog signals being
received or generated by interface module 110, e.g., radiometer
signal(s), a thermocouple signal, the ablation energy power, and/or
the temperature calculated by processor 210.
[0059] So as to inhibit potential degradations in the performance
of processor 210, memory 230, or user interface 280 resulting from
electrical contact with RF energy, interface module 110 may include
opto-electronics 299 that communicate information to and from
processor 210, but that substantially inhibit transmission of RF
energy to processor 210, memory 230, or user interface 280. This
isolation is designated by the dashed line in FIG. 2A. For example,
opto-electronics 299 may include circuitry that is in operable
communication with first I/O port 201 so as to receive the digital
TC and radiometer signals from first I/O port 201, and that
converts such digital signals into optical digital signals.
Opto-electronics 299 also may include an optical transmitter in
operable communication with such circuitry, that transmits those
optical digital signals to processor 210 through free space.
Opto-electronics 299 further may include an optical receiver in
operable communication with processor 210, that receives such
optical digital signals, and circuitry that converts the optical
digital signals into digital signals for use by processor 210. The
opto-electronic circuitry in communication with the processor also
may be in operable communication with a second optical transmitter,
and may receive signals from processor 210 to be transmitted across
free space to an optical receiver in communication with the
circuitry that receives and processes the digital TC and radiometer
signals. For example, processor 210 may transmit to such circuitry,
via an optical signal, a signal that causes the circuitry to
generate an analog version of the TC signal and to provide that
analog signal to the second I/O port. Because opto-electronic
circuitry, transmitters, and receivers are known in the art, its
specific components are not illustrated in FIG. 2A.
[0060] With respect to FIG. 2B, additional internal components of
interface module 110 of FIG. 2A are described, as well as selected
connections to and from the interface module. FIG. 2B is an
exemplary schematic for a grounding and power supply scheme
suitable for using interface module 110 with an RF electrosurgical
generator, e.g., a Stockert EP-Shuttle or 70 RF Generator. Other
grounding and power supply schemes suitably may be used with other
types, makes, or models of electrosurgical generators, as will be
appreciated by those skilled in the art.
[0061] As illustrated in FIG. 2B, interface module 110 includes
isolated main power supply 205 that may be connected to standard
three-prong A/C power outlet 1, which is grounded to mains ground
G. Interface module 110 also includes several internal grounds,
designated A, B, C, and I. Internal ground A is coupled to the
external mains ground G via a relatively small capacitance
capacitor (e.g., a 10 pF capacitor) and a relatively high
resistance resistor (e.g., a 20 M.OMEGA. resistor) that
substantially prevents internal ground A from floating. Internal
ground B is coupled to internal ground A via a low resistance
pathway (e.g., a pathway or resistor(s) providing less than
1000.OMEGA. resistance, e.g., about 0 .OMEGA./resistance).
Similarly, internal ground C is coupled to internal ground B via
another low resistance pathway. Internal ground I is an isolated
ground that is coupled to internal ground C via a relatively small
capacitance capacitor (e.g., a 10 pF capacitor) and a relatively
high resistance resistor (e.g., a 20 M.OMEGA. resistor) that
substantially prevents isolated ground I from floating.
[0062] Isolated main power supply 205 is coupled to internal ground
A via a low resistance pathway. Isolated main power supply 205 is
also coupled to, and provides power (e.g., .+-.12V) to, one or more
internal isolated power supplies that in turn provide power to
components internal to interface module 110. Such components
include, but are not limited to components illustrated in FIG. 2A.
For example, interface module 110 may include one or more isolated
power supplies 220 that provide power (e.g., .+-.4V) to processor
210, memory 230, and analog circuitry 240. Analog circuitry 240 may
include components of user interface 280, including temperature
display 113 and circuitry that appropriately prepares signals for
output on data ports 114. Data ports 114, as well as analog
circuitry 240, are coupled to internal ground B via low resistance
pathways, while processor and memory 210, 230 are coupled to
internal ground C via low resistance pathways. Interface module
also may include one or more isolated power supplies 270 that
provide power (e.g., .+-.4V) to ICT 122, PIM 121, and RF circuitry
290.
[0063] RF circuitry 290 may include patient and load relays 250,
260, as well as circuitry that receives the radiometer and
thermocouple signals and provides such signals to the processor via
optoelectronic coupling, and circuitry that generates a clock
signal to be provided to the ICT as described further below with
reference to FIG. 5B. RF circuitry 290, ICT 122, and PIM 121 are
coupled to isolated internal ground I via low resistance
pathways.
[0064] As shown in FIG. 2B, power supply 139 of RF electrosurgical
generator 130, which may be external to generator 130 as in FIG. 2B
or may be internal to generator 130, is connected to standard two-
or three-prong A/C power outlet 2. However, generator power supply
139 is not connected to the ground of the outlet, and thus not
connected to the mains ground G, as is the isolated main power
supply. Instead, generator power supply 139 and RF electrosurgical
generator 130 are grounded to internal isolated ground I of
interface module 110 via low resistance pathways between generator
130 and PIM 121 and ICT 122, and low resistance pathways between
PIM 121 and ICT 122 and internal isolated ground I. As such, RF
circuitry 290, PIM 121, IE 140, and generator 130 are all
"grounded" to an internal isolated ground I that has essentially
the same potential as does ICT 122. Thus, when RF energy is applied
to ICT 122 from generator 130 through interface module 110, the
ground of RF circuitry 290, PIM 121, ICT 122, IE 140, and generator
130 all essentially float with the RF energy amplitude, which may
be a sine wave of 50-100V at 500 kHz.
[0065] As further illustrated in FIG. 2B, the .+-.12V of power that
isolated main power supply 205 provides to isolated
processor/memory/analog power supply 220 and to isolated ICT/RF
power supply 270 may be coupled by parasitic capacitance (pc,
approximately 13 pF) to A/C power outlet 1, as may be the .+-.4V of
power that such power supplies provide to their respective
components. Such parasitic coupling will be familiar to those
skilled in the art. Note also that the particular resistances,
capacitances, and voltages described with reference to FIG. 2B are
purely exemplary and may be suitably varied as appropriate to
different configurations.
[0066] FIG. 2C schematically illustrates components of temperature
control subsystem 119, which as noted above may be connected to one
or more data ports 114 of interface module 110 via control cable
136 (FIGS. 1A-1B), or alternatively may be included within the
housing of interface module 110 (FIGS. 1D-1E). In the illustrated
embodiment, temperature control subsystem 119 includes input
port(s) 212, processor 211, memory 235, user input 285, and display
286. Temperature control subsystem 119 is connected to power
control interface 290 via power control cable 137, although power
control interface 290 alternatively may be integrated with
temperature control subsystem 119 and/or interface module 110
(FIGS. 1C and 1E). Note that the functionalities of processor 210
of interface module 110 and processor 211 of temperature control
subsystem 119 optionally may both be provided by a single
processor, particularly (but not necessarily) in embodiments where
interface module 110 and temperature control subsystem 119 are
integrated with one another (FIGS. 1D-1E). Additionally, or
alternatively, the functionalities of memory 230 of interface
module 110 and memory 235 of temperature control subsystem 119 may
both be provided by a single memory, particularly (but not
necessarily) in embodiments where interface module 110 and
temperature control subsystem 119 are integrated with one another
(FIGS. 1D-1E).
[0067] As illustrated in FIG. 2C, temperature control subsystem 119
receives on input port(s) 212, from data port 114, the temperature
calculated by processor 210 based on signal(s) from the radiometer,
as well as the power of the ablation energy being transmitted to
the ICT 122 via first I/O port 201 of interface module 110. An
appropriate ablation energy power meter may be provided within
interface module 110 for such purpose.
[0068] Memory 235 of temperature control subsystem 119, which may
be any suitable persistent, computer-readable medium, stores
setpoint 281, ablation time 282, feedback parameters 283, and
temperature control module 284. Setpoint 281 is a target
temperature at which a region of tissue is to be ablated during an
ablation procedure, e.g., 55.degree. C. for a cardiac hyperthermia
ablation procedure. Ablation time 282 is a target time for which
the region of tissue is to be ablated once the target temperature
is reached, e.g., 60 seconds for a cardiac hyperthermal ablation
procedure performed at 55.degree. C. Note that appropriate
setpoints and times may vary depending on the particular type of
ablation being performed (e.g., hypothermia, hyperthermia), as well
as the location in the heart where the ablation is being performed.
Setpoint 281 and/or ablation time 282 may be pre-determined, or
alternatively may be input by a clinician via user input 285.
Ablation time 282 alternatively may be omitted from temperature
control subsystem 119, and the ablation time controlled via
ablation energy generator 130 as described above. Temperature
control subsystem 119 may display to the clinician the calculated
temperature, the power of ablation energy, setpoint 281, and/or
ablation time 282 via display 286, which may be a single-color or
multi-color digital display such as an LCD or LED.
[0069] Feedback parameters 283 define the feedback characteristics
of the power regulation that temperature control subsystem 119
provides. For example, parameters 283 may include a slope with
which the power is to be ramped, as well as under-shoot/over-shoot
parameters that prevent the power from being ramped to too low or
too high a power due to delays in the temperature as the tissue
responds to the applied ablation energy. Optionally, one or more of
parameters 283 may be adjusted by the clinician via user input 285
and/or displayed to the clinician via display 286. Temperature
control module 284 contains a set of instructions that cause
processor 211 to regulate the power of ablation energy based on the
setpoint 281 and feedback parameters 282 stored in memory 235 and
the calculated temperature and ablation energy power signals
received on input port(s) 212 from data ports 114. Such
instructions may include steps such as described further below with
respect to FIGS. 3A and 3C.
[0070] Temperature control subsystem 119 further is in operable
communication with power control interface 290 via power control
cable 137. Power control interface 290 is configured to be operably
coupled to an adjustable power control of electrosurgical generator
130. For example, electrosurgical generator 130 may include an I/O
port (not illustrated) through which generator 130 may receive
suitable control signals that define a power at which the generator
outputs ablation energy, and power control interface 290 may
include a control signal generator that generates suitable control
signals and passes those control signals to the generator via an
I/O port connected to the port of the generator.
[0071] Alternatively, as illustrated in FIG. 1A, electrosurgical
generator 130 may include a power control knob 132 that, during a
conventional procedure, a clinician uses to manually adjust the
ablation energy power. In some embodiments, the power control
interface 290 of temperature control subsystem 119 may include a
suitable mechanism for mechanically controlling the ablation energy
power via such a power control knob 132. For example, as
illustrated in FIG. 2D, power control interface 290 may include
stepper motor 291, which is coupled to power control knob 132 (not
visible in FIG. 2D) of generator 130 via spring-loaded knob
adjuster 292, and which is coupled to temperature control subsystem
119 via power control cable 137. Stepper motor 291 and
spring-loaded knob adjuster 292 may be held in place by bracket
293. Stepper motor 291 includes an on-board mini-controller (not
shown) that, responsive to instructions from processor 211 provided
via cable 137, rotates knob adjuster 292. Knob adjuster 292 is
spring-loaded so as to apply pressure to the face of knob 132, such
that rotation of knob adjuster 292 causes knob 132 to rotate and
thus to increase or decrease the ablation energy power by an amount
determined by processor 211 based on the above-noted inputs and
parameters. Preferably, knob 132 also may be manually adjusted even
when power control interface 290 is in place, such that a clinician
may rapidly intervene and manually adjust the ablation energy power
as needed during an ablation procedure. Note that although FIG. 2D
depicts interface module 110, temperature control subsystem 119,
and power control interface 290 as being separate elements from one
another connected via appropriate cabling, consistent with FIGS.
1A-1B, such elements alternatively may be partially or fully
integrated with one another such as described above with reference
to FIGS. 1C-1E.
[0072] Referring now to FIG. 3A, method 300 of using interface
module 110, temperature control subsystem 119, and power control
interface 290 of FIGS. 1A-2D during a tissue ablation procedure is
described. The clinician may couple the integrated catheter tip
(ICT) 122 and indifferent electrode (IE) 140 to respective I/O
ports of interface module 110 (step 301). For example, as shown in
FIG. 1A, ICT 122 may be coupled to a first connector on front panel
111 of interface module 110 via patient interface module (PIM) 121,
and IE 140 may be coupled to a third connector on front panel 111
via indifferent electrode cable 141. The first connector is in
operable communication with first I/O port 201 (see FIG. 2A) and
the third connector is in operable communication with third I/O
port 203 (see FIG. 2A).
[0073] In FIG. 3A, the clinician may couple temperature control
subsystem 119 to interface module 110 and power control interface
290, and may couple power control interface 290 to the power
control of electrosurgical generator 130 (step 302). For example,
as illustrated in FIGS. 1A and 2D, temperature control subsystem
119 may be coupled to data port(s) 114 of interface module 110 via
temperature control cable 136 and may be coupled to power control
interface 290 via power control cable 137. Power control interface
290 may be coupled to power control knob 132 of electrosurgical
generator 130. Note that if interface module 110, temperature
control subsystem 119, and/or power control interface 290 are
partially or fully integrated with one another, then the clinician
need not separately provide connections between them. Additionally,
if electrosurgical generator 130 accepts suitable control signals
to adjust the ablation energy power, then the power control
interface 290 may be coupled to the generator via appropriate
cabling, rather than by a mechanical interface such as stepper
motor 291.
[0074] In FIG. 3A, the clinician may couple electrosurgical
generator 130 to I/O port(s) of interface module 110 (step 303).
For example, as illustrated in FIG. 1A, electrosurgical generator
130 may be coupled to a second connector on back panel 112 of
interface module 110 via connection cable 135, and also may be
coupled to a fourth connector on back panel 112 via indifferent
electrode cable 134. The second connector is in operable
communication with second I/O port 202 (see FIG. 2A), and the
fourth connector is in operable communication with fourth I/O port
204 (see FIG. 2A).
[0075] In FIG. 3A, the clinician initiates flow of irrigant,
positions ICT 122 within the subject, e.g., in the subject's heart,
and positions IE 140 in contact with the subject, e.g., on the
subject's back (step 304). Those skilled in the art will be
familiar with methods of appropriately positioning catheter tips
relative to the heart of a subject in an ablation procedure, for
example via the peripheral arterial or venous vasculature.
[0076] Interface module 110 receives digital radiometer, digital
thermocouple, and/or analog ECG signals from ICT 122, and receives
ablation energy from generator 130 (step 305), for example using
the connections, ports, and pathways described above with
references to FIGS. 1A-2D. Preferably, generator 130 may provide
such ablation energy to interface module 110 responsive to the
clinician pressing "start" using inputs 133 on the front face of
generator 130 (see FIG. 1A).
[0077] Interface module 110 calculates and displays the temperature
adjacent to ICT 122, based on the radiometer and thermocouple
signals (step 306). This calculation may be performed, for example,
by processor 210 based on instructions in temperature calculation
module 233 stored in memory 230 (see FIG. 2A). Exemplary methods of
performing such a calculation are described in greater detail below
with respect to FIG. 3B.
[0078] In method 300, interface module 100 also actuates patient
relay 250 so as to provide ablation energy to ICT 122 for use in
tissue ablation (step 307). For example, processor 210 maintain
patient relay 250 illustrated in FIG. 2A in a normally closed state
during operation, such that ablation energy flows from
electrosurgical generator 130 to ICT 122 through interface module
110 without delay upon the clinician's actuation of the generator,
and may open patient relay 250 only upon detection of unsafe
conditions such as described below with respect to FIG. 3C. In an
alternative embodiment, processor 210 may maintain patient relay
250 in a normally open state during operation, and may determine
based on instructions in decision module 234 and on the temperature
calculated in step 305 that it is safe to proceed with the tissue
ablation, and then close patient relay so as to pass ablation
energy to the ICT. In either case, after a time period defined
using input 133 on the front face of generator 130, the supply of
ablation energy ceases or the clinician manually turns off the
supply of ablation energy.
[0079] Interface module 110 also generates an analog version of the
thermocouple signal, and provides the ECG and analog thermocouple
signals to generator 130 (step 308). Preferably, step 308 is
performed continuously by the interface module throughout steps 304
through 307, rather than just at the end of the ablation procedure.
For example, as will be familiar to those skilled in the art, the
Stockert EP-Shuttle or 70 RF Generator may "expect" certain signals
to function properly, e.g., those signals that the generator would
receive during a standard ablation procedure that did not include
use of interface module 110. The Stockert EP-Shuttle or 70 RF
generator requires as input an analog thermocouple signal, and
optionally may accept analog ECG signal(s). The interface module
110 thus may pass through the ECG signal(s) generated by the ICT to
the Stockert EP-shuttle or 70 RF generator via second I/O port 202.
However, as described above with reference to FIG. 2A, interface
module 110 receives a digital thermocouple signal from ICT 122. In
its standard configuration, the Stockert EP-Shuttle or 70 RF
generator is not configured to receive or interpret a digital
thermocouple signal. As such, interface module 110 includes the
functionality of reconstituting an analog version of the
thermocouple signal, for example using processor 210 and
opto-electronics 299, and providing that analog signal to generator
130 via second I/O port 202.
[0080] In FIG. 3A, temperature control module 119 then regulates
the power of ablation energy provided to ICT 122 based on the
calculated temperature and on a setpoint, i.e., a target ablation
temperature, via power control interface 290 (step 309). For
example, as discussed above with respect to FIGS. 2C-2D,
temperature control module 119 receives calculated temperature and
ablation energy power signals from interface module 110, e.g., via
data port(s) 114. Based on the received signals, stored setpoint
281, stored ablation time 282, stored feedback parameters 283, and
instructions in temperature control module 284, processor 211 of
subsystem 119 determines a power and time at which ablation energy
should be provided to the tissue, for example using PI
(proportional-integral) or PID (proportional-integral-derivative)
control loop feedback algorithms such as known in the art. Then,
processor 211 causes power control interface 290 to regulate the
ablation energy power generated by generator 130 so as to achieve
the power, e.g., by generating an appropriate control signal or by
mechanically adjusting the power knob on the face of generator 130.
Responsive to the regulation of the ablation energy power, the
tissue temperature may change, resulting in changes to the digital
radiometer and/or digital thermocouple signals from the ICT (step
305). The new temperature may be calculated based on the changed
signals (step 306) and the ablation energy power provided to the
ICT regulated based on the new temperature (step 309). As such, the
ablation energy power may be dynamically and automatically
controlled during the ablation procedure so as to substantially
continuously maintain the tissue temperature at or near the
setpoint for a desired amount of time, e.g., using PI or PID
control loop feedback algorithms.
[0081] Turning to FIG. 3B, the steps of method 350 of calculating
radiometric temperature using digital signals from a radiometer and
a thermocouple and operation parameters is described. The steps of
the method may be executed by processor 210 based on temperature
calculation module 233 stored in memory 230 (see FIG. 2A). While
some of the signals and operation parameters discussed below are
particular to a PIM and ICT configured for use with RF ablation
energy, other signals and operation parameters may be suitable for
use with a PIM and ICT configured for use with other types of
ablation energy. Those skilled in the art will be able to modify
the systems and methods provided herein for use with other types of
ablation energy.
[0082] In FIG. 3B, processor 210 of interface module 110 obtains
from memory 230 the operation parameters for the thermocouple (TC)
and the radiometer (step 351). These operation parameters may
include, for example, TCSlope, which is the slope of the TC
response with respect to temperature; TCOffset, which is the offset
of the TC response with respect to temperature; RadSlope, which is
the slope of the radiometer response with respect to temperature;
TrefSlope, which is the slope of a reference temperature signal
generated by the radiometer with respect to temperature; and F,
which is a scaling factor.
[0083] Processor 210 then obtains via first I/O port 201 and
opto-electronics 299 the raw digital signal from the thermocouple,
TCRaw (step 352), and calculates the thermocouple temperature, TCT,
based on TCRaw using the following equation (step 353):
TCT = TCR aw TCSlope - TCOffset ##EQU00001##
[0084] Then, processor 210 causes temperature display 113 to
display TCT until both of the following conditions are satisfied:
TCT is in the range of 35.degree. C. to 39.degree. C., and ablation
energy is being provided to the ICT (e.g., until step 307 of FIG.
3A). There are several reasons to display only the thermocouple
temperature TCT, as opposed to the temperature calculated based on
signal(s) from the radiometer, until both of these conditions are
satisfied. For example, if the temperature TCT measured by the
thermocouple is less than 35.degree. C., then based on instructions
in decision module 234 the processor 210 interprets that
temperature as meaning that ICT 122 is not positioned within a
living human body, which would have a temperature of approximately
37.degree. C. If ICT 122 is not positioned within a living human
body, then it would be unsafe to provide power to the radiometer
circuitry, as it may rapidly burn out if powered on in air as
opposed to blood.
[0085] Processor 210 then provides ablation energy to ICT 122,
e.g., in accordance with step 307 described above, and receives via
second I/O port 202 two raw digital signals from the radiometer:
Vrad, which is a voltage generated by the radiometer based on the
temperature adjacent the ICT; and Vref, which is a reference
voltage generated by the radiometer (step 355). Processor 210
calculates the reference temperature Tref based on Vrefusing the
following equation (step 356):
Tref = Vref TrefSlope + TrefOffset ##EQU00002##
[0086] Processor 210 also calculates the radiometric temperature
Trad based on Vrad and Tref using the following equation (step
357):
Trad = Vrad RadSlope - RadOffset + Tref ##EQU00003##
[0087] During operation of interface module 110, processor 210 may
continuously calculate TCT, and also may continuously calculate
Tref and Trad during times when ablation power is provided to the
ICT (which is subject to several conditions discussed further
herein). Processor 210 may store in memory 230 these values at
specific times and/or continuously, and use the stored values to
perform further temperature calculations. For example, processor
210 may store in memory 230 TCT, Tref, and Trad at baseline, as the
respective values TCBase, TrefBase, and TradBase. The processor
then re-calculates the current radiometric temperature TradCurrent
based on the current Vrad received on second I/O port 202, but
instead with reference to the baseline reference temperature
TrefBase, using the following equation (step 358):
TradCurrent = Vrad RadSlope - RadOffset + TrefBase ##EQU00004##
[0088] Processor 210 then calculates and causes temperature display
113 to display a scaled radiometric temperature TSrad for use by
the clinician based on the baseline thermocouple temperature
TCBase, the baseline radiometer temperature TradBase, and the
current radiometer temperature TradCurrent, using the following
equation (step 359):
TSrad=TCBase+(TradCurrent-TradBase).times.F
[0089] In this manner, interface module 110 displays for the
clinician's use a temperature calculated based on signal(s) from
the radiometer that is based not only on voltages generated by the
radiometer and its internal reference, described further below with
reference to FIGS. 6A-6B, but also on temperature measured by the
thermocouple.
[0090] With respect to FIG. 3C, method 360 of controlling an
ablation procedure based on a temperature calculated based on
signal(s) from a radiometer, e.g., as calculated using method 350
of FIG. 3B, and also based on safety parameters 232 and decision
module 234 stored in memory 230 of interface module 110 (FIG. 2A)
and setpoint 281, ablation time 282, feedback parameters 283, and
instructions in temperature control module 284 stored in memory 235
of temperature control subsystem 119, will now be described.
[0091] In method 360 of FIG. 3C, a slow flow of irrigant is
initiated through ICT 122, and the ICT is then positioned within
the subject (step 361). For example, in embodiments using a
Stockert 70 RF Generator 130, the generator may automatically
initiate slow irrigant flow to catheter tip 122 by sending
appropriate signals to a CoolFlow irrigant pumping system 150
associated with the generator, responsive to actuation of the
generator by the clinician.
[0092] The clinician presses a button on generator 130 to start the
flow of ablation energy to ICT 122; this may cause the generator to
initiate a high flow of irrigant to the ICT and generation of
ablation energy following a 5 second delay (step 362). Interface
module 110 passes the ablation energy to ICT 122 via patient relay
250, as described above with respect to step 307 of FIG. 3A.
[0093] Based on the calculated and displayed temperature (see
methods 300 and 350 described above with respect to FIGS. 3A-3B),
the clinician determines the temperature of the tissue volume that
is being ablated by the ablation energy (step 363). By comparison,
temperature measured by a thermocouple alone would provide little
to no useful information during this stage of the procedure.
[0094] Then, based on the calculated temperature, the power of
ablation energy is automatically regulated so as to achieve the
setpoint temperature, e.g., using temperature control subsystem 119
and power control interface 290 (step 364). Based on such
regulation, the tissue temperature may change, which change is
measured at step 363; the power of ablation energy may further be
regulated based on such changes in the calculated tissue
temperature.
[0095] Interface module 110 further may use the calculated
radiometric temperature to determine whether the ablation procedure
is being performed within safety parameters. For example, processor
210 may obtain safety parameters 232 from memory 230. Among other
things, these safety parameters may include a cutoff temperature
above which the ablation procedure is considered to be "unsafe"
because it may result in perforation of the cardiac tissue being
ablated, with potentially dire consequences. The cutoff temperature
may be any suitable temperature below which one or more unsafe
conditions may not occur, for example "popping" such as described
below with respect to FIGS. 4E-4F, or tissue burning, but at which
the tissue still may be sufficiently heated. One example of a
suitable cutoff temperature is 85.degree. C., although higher or
lower cutoff temperatures may be used, e.g., 65.degree. C.,
70.degree. C., 75.degree. C., 80.degree. C., 90.degree. C., or
95.degree. C. Instructions in decision module 234, also stored in
memory 230, cause processor 210 to continuously compare the
calculated radiometric temperature to the cutoff temperature, and
if the radiometric temperature exceeds the cutoff temperature, the
processor may set an alarm, open the patient relay, and close the
load relay so as to return power to the IE via I/O port 204,
thereby cutting off flow of ablation energy to the ICT (step 365 of
FIG. 3C). Otherwise, the processor may allow the ablation procedure
to proceed (step 365).
[0096] The ablation procedure terminates (step 366), for example,
when the clinician presses the appropriate button on generator 130,
or when the generator 130 automatically cuts of ablation energy at
the end of a predetermined period of time.
[0097] Referring now to FIGS. 4A-4F, illustrative data obtained
during ablation experiments using interface module 110, optionally
with temperature control subsystem 119, and power control interface
290 constructed and operated in accordance with the present
invention will now be described. This data was obtained using an
unmodified Stockert EP Shuttle Generator with integrated irrigation
pump, and a catheter including the PIM 121 and ICT 122 described
further below with reference to FIGS. 5A-6B.
[0098] FIG. 4A illustrates the change over time in various signals
collected during an ablation procedure in which ICT 122 was placed
against exposed thigh tissue of a living dog, and the Stockert EP
Shuttle generator manually actuated so as to apply 20W of RF energy
for 60 seconds. A Luxtron probe was also inserted at a depth of 3
mm into the dog's thigh. Luxtron probes are considered to provide
accurate temperature information, but are impractical for normal
use in cardiac ablation procedures because such probes cannot be
placed in the heart of a living being. In this procedure,
temperature control subsystem 119 and power control interface 290
were not used, but the data is explained with the intention of
orienting the reader as to signals that may be generated during an
ablation procedure performed using interface module 110; data
obtained during temperature-controlled procedures, in which
temperature control subsystem 119 and power control interface 290
were used with interface module 110 is provided further below with
reference to FIGS. 4B-4C.
[0099] In FIG. 4A, signal 401 corresponds to scaled radiometric
temperature TSrad; signal 402 corresponds to the thermocouple
temperature; signal 403 corresponds to a temperature measured by
the Luxtron probe; and signal 404 corresponds to the power
generated by the Stockert EP Shuttle Generator. As can be seen from
FIG. 4A, power signal 404 indicates that RF power was applied to
the subject's tissue beginning at a time of about 40 seconds and
ending at a time of about 100 seconds. Radiometric temperature
signal 401 indicates a sharp rise in temperature beginning at about
40 seconds, from a baseline in region 405 of about 28.degree. C. to
a maximum in region 406 of about 67.degree. C., followed by a
gradual fall in region 407 beginning around 100 seconds. The
features of radiometric temperature signal 401 are similar to those
of Luxtron probe signal 403, which similarly shows a temperature
increase beginning around 40 seconds to a maximum value just before
100 seconds, and then a temperature decrease beginning around 100
seconds. This similarity indicates that the calculated radiometric
temperature 401 has similar accuracy to that of the Luxtron probe
403. By comparison, thermocouple signal 402 shows a significantly
smaller temperature increase beginning around 40 seconds, followed
by a low-level plateau in the 40-100 second region, and then a
decrease beginning around 100 seconds. The relatively weak response
402 of the thermocouple, and the relatively strong and accurate
response of the calculated radiometric temperature 401, indicate
that an unmodified Stockert EP Shuttle Generator successfully may
be retrofit using interface module 110 constructed in accordance
with the principles of the present invention to provide a clinician
with useful radiometric temperature information for use in an
ablation procedure.
[0100] FIG. 4B illustrates signals obtained during a similar
experimental procedure performed in the thigh of a living dog, but
in which temperature control subsystem 119 and power control
interface 290 configured illustrated in FIGS. 1A-1B and 2C-2D were
coupled to interface module 110 and used to automatically regulate
the ablation power provided to the animal's tissue to a setpoint
(target ablation temperature) of 80.degree. C. for about 80
seconds. In FIG. 4B, signal 411 corresponds to scaled radiometric
temperature TSrad; signal 412 corresponds to the thermocouple
temperature; signal 413 corresponds to a temperature measured by
the Luxtron probe; signal 414 corresponds to the power generated by
the Stockert EP Shuttle Generator; signal 415 corresponds to the
measured tissue impedance; and signal 416 corresponds to Vrad.
[0101] In FIG. 4B, beginning around 19 seconds, power signal 414
may be seen to increase to a maximum of approximately 42 watts as
the scaled radiometric temperature signal 411 increases from about
36.degree. C. to about 84.degree. C., and the Luxtron probe signal
413 increases from about 29.degree. C. to about 84.degree. C.,
while the thermocouple temperature 412 does not significantly
change. Oscillations 417 may be seen between about 25 and 40
seconds in power signal 414 and correspond to rapid adjustments
that temperature control subsystem 119 makes to the ablation power,
via power control interface 290, responsive to changes in the
scaled radiometric temperature signal 411. Between about 40-120
seconds, power signal 414 then decreases to and stabilizes at about
25 watts, representing the reduced power required to maintain the
tissue near the setpoint temperature (rather than to heat the
tissue to that temperature, which requires additional power).
During the same time period, scaled radiometric temperature signal
411 may be seen to stabilize at about 80.degree. C., and Luxtron
probe signal 413 to stabilize at around 82.degree. C. At around 120
seconds, the ablation power is reduced to zero with concomitant
reduction in power signal 414, and thereafter the scaled
radiometric temperature signal 411 and Luxtron probe signal 413 may
be seen to gradually decrease back to body temperature. Impedance
signal 415 may be seen to increase and then stabilize during
application of ablation power between about 19-120 seconds, while
Vrad signal 416 may be seen to decrease during this time
period.
[0102] FIG. 4C illustrates signals obtained during a similar
experimental procedure performed in the beating of a living dog,
and in which temperature control subsystem 119 and power control
interface 290 configured illustrated in FIGS. 1A-1B and 2C-2D were
coupled to interface module 110 and used to automatically regulate
the ablation power provided to the animal's tissue to a setpoint
(target ablation temperature) of 80.degree. C. for about 60
seconds. In FIG. 4C, signal 421 corresponds to scaled radiometric
temperature TSrad; signal 422 corresponds to the thermocouple
temperature; signal 424 corresponds to the power generated by the
Stockert EP Shuttle Generator; signal 425 corresponds to the
measured tissue impedance; and signal 426 corresponds to Vrad. A
Luxtron probe was not used during this procedure because it was
performed in a beating heart.
[0103] In FIG. 4C, beginning around 18 seconds, power signal 424
may be seen to increase to a maximum of approximately 30 watts as
the scaled radiometric temperature signal 421 increases from about
40.degree. C. to about 85.degree. C., while the thermocouple
temperature 422 does not significantly change. Oscillations 427 may
be seen between about 25 and 45 seconds in power signal 424 and
correspond to rapid adjustments that temperature control subsystem
119 makes to the ablation power, via power control interface 290,
responsive to changes in the scaled radiometric temperature signal
421. Between about 45-78 seconds, power signal 424 then decreases
to and stabilizes at about 17 watts, representing the reduced power
required to maintain the tissue near the setpoint temperature
(rather than to heat the tissue to that temperature, which requires
additional power). During this same time period, scaled radiometric
temperature signal 421 may be seen to stabilize at about 80.degree.
C. At around 78 seconds, the ablation power is reduced to zero with
concomitant reduction in power signal 424, and thereafter the
scaled radiometric temperature signal 421 may be seen to gradually
decrease back to body temperature. Impedance signal 425 may be seen
to increase and then stabilize during application of ablation power
between about 18-78 seconds, while oscillating as a result of the
beating of the heart, while Vrad signal 426 may be seen to decrease
and oscillate during this time period.
[0104] Additional experimental data obtained during other
procedures in which temperature control subsystem 119 and power
control interface 290 were not used will now be described with
reference to FIGS. 4D-4F, so as to more fully explain the
functionality of interface module 110. It will be appreciated that
coupling interface module 110 to temperature control subsystem 119
and power control interface 290 may provide additional enhanced
functionalities, including temperature control, such as described
further above.
[0105] FIG. 4D illustrates signals obtained during an experimental
procedure similar to that described above with reference to FIG.
4A, and in which two Luxtron probes were implanted into the thigh
tissue of a living dog, the first at a depth of 3 mm and the second
at a depth of 7 mm. The Stockert EP Shuttle generator was
activated, and the RF power was manually modulated between 5 and 50
W using power control knob 132 on the front panel of the generator.
In FIG. 4D, the scaled radiometric temperature signal is designated
431, the 3 mm Luxtron signal designated 432, and the 7 mm Luxtron
designated 433. The scaled radiometric temperature signal 431 and
the 3 mm Luxtron signal 432 may be seen to have relatively similar
changes in amplitude to one another resulting from the periodic
heating of the tissue by RF energy. The 7 mm Luxtron signal 433 may
be seen to have a slight periodicity, but far less modulation than
do the radiometric temperature and 3 mm Luxtron signals 431, 432.
This is because the 7 mm Luxtron is sufficiently deep within the
tissue that ablation energy substantially does not directly
penetrate at that depth. Instead, the tissue at 7 mm may be seen to
slowly warm as a function of time, as heat deposited in shallower
portions of the tissue gradually diffuses to a depth of 7 mm.
[0106] FIGS. 4A-4F illustrate data obtained during a series of
cardiac ablation procedures that were also performed in living
humans using the experimental setup described above with respect to
FIG. 4C, but omitting temperature control subsystem 119 and power
control interface 290. The humans all suffered from atrial flutter,
were scheduled for conventional cardiac ablation procedures for the
treatment of same, and consented to the clinician's use of the
interface box and ICT during the procedures. The procedures were
performed by a clinician who introduced the ICT into the
individuals' endocardia using conventional methods. During the
procedures, the clinician was not allowed to view the temperature
calculated by the interface module. As such, the clinician
performed the procedures in the same manner as they would have done
with a system including a conventional RF ablation catheter
directly connected to a Stockert EP-Shuttle generator. The
temperature calculated by the interface module during the various
procedures was made available for the clinician to review at a
later time. The clinician performed a total of 113 ablation
procedures on five humans using the above-noted experimental
setup.
[0107] FIG. 4E illustrates the change over time in signal 441
corresponding to the scaled radiometric temperature TSrad, as well
as the change over time in the signal 442 corresponding to the
thermocouple temperature, during the tenth ablation procedure
performed on the individual. During the procedure, about 40 W of RF
power was applied to the individual's cardiac tissue for 60 seconds
(between about 20 seconds and 80 seconds in FIG. 4E), and the
clinician had a target temperature 445 of 55.degree. C. to which it
was desired to heat the cardiac tissue so as to sufficiently
interrupt an aberrant pathway causing the individual's atrial
flutter. It can be seen that the scaled radiometric temperature
signal 441, which was subjected to data smoothing in FIG. 4E,
varied between about 40.degree. C. and 51.degree. C. while RF power
was applied and manually controlled by the clinician via control
knob 132. By comparison, as expected, the thermocouple temperature
442 provided essentially no useful information about the tissue
temperature during the procedure. Notably, the clinician's target
temperature 445 of 55.degree. C. was never reached during the
procedure, even though the clinician believed based on his or her
perceptions of the procedure that such temperature had been reached
by manually adjusting the RF power via control knob 132. Because
the target temperature 445 was not reached, the tissue was
insufficiently heated during the procedure to interrupt an aberrant
pathway. The failure to reach the target temperature may be
attributed to insufficient contact and/or force between the
ablative tip of the ICT and the individual's cardiac tissue, the
condition of the cardiac surface, insufficient power, and the
like.
[0108] FIG. 4F illustrates the change over time in signal 451
corresponding to TSrad, as well as the change over time in signal
452 corresponding to the thermocouple temperature, during the
eleventh ablation procedure performed on the same individual as in
FIG. 4E. During this procedure, again about 40W of RF power was
applied to the individual's cardiac tissue for 60 seconds (between
about 20 seconds and 80 seconds in FIG. 4E), and the clinician
again had a target temperature 455 of 55.degree. C. It can be seen
that the scaled radiometric signal 451, again subject to data
smoothing, varied between about 55.degree. C. and 70.degree. C.
while RF power was applied and manually controlled by the clinician
via control knob 132, while the thermocouple temperature 452 again
provided essentially no useful information. Here, the clinician
attributed the higher temperature tissue temperature achieved
during the ablation to better contact between the ablative tip of
the ICT and the individual's cardiac tissue. However, it can be
seen that even while RF power was being applied to the tissue, the
temperature varied relatively rapidly over time, e.g., from about
70.degree. C. at about 35 seconds, to about 56.degree. C. at 40
seconds, which may be attributed to variations in the quality of
contact between the ICT and the individual's cardiac tissue.
[0109] The results of the ablation procedures performed on the five
individuals are summarized in the following table:
TABLE-US-00001 Total % of Total Ablation Number of patients 5
Number of ablations 113 Number of ablations that did not 50 44%
reach target temperature of 55.degree. C. Number of ablations that
reached 13 12% high temperature cutoff of 95.degree. C. Number of
pops 3 3% Number of successful treatments 5 100% of atrial
flutter
[0110] As can be seen from the above table, 44% of the ablation
procedures did not reach the clinician's target tissue temperature
of 55.degree. C. As such, it is likely that this percentage of the
procedures resulted in insufficient tissue heating to interrupt
aberrant pathway(s). However, although many of the ablation
procedures failed, the clinician repeated the ablation procedures a
sufficient number of times to achieve 100% treatment of the
individuals' atrial flutter. It is believed that displaying the
calculated temperature to the clinician during ablation procedures
would enable the clinician to far more accurately assess the
quality of contact between the ablative tip of the ICT and the
individual's cardiac tissue, and thus to sufficiently heat the
tissue above the target temperature for a desired period of time,
and thus reduce the clinicians' need to repeatedly perform numerous
ablation procedures on the same subject so as to achieve the
desired treatment. Moreover, it is believed that automatically
controlling the ablation power during ablation procedures would
provide the clinician with greater control over lesion formation,
thus improving the percentage of effective lesions and reducing the
incidence of pops and burns.
[0111] As shown in the above table, 12% of the ablation procedures
triggered the high temperature cutoff such as illustrated in FIG.
3C. Here, the cutoff temperature was defined to be 95.degree. C.
However, it was observed that at this cutoff temperature, "pops"
formed during three of the ablation procedures. A "pop" occurs when
the blood boils because of excessive localized heating caused by
ablation energy, which results in formation of a rapidly expanding
bubble of hot gas that may cause catastrophic damage to the cardiac
tissue. It is believed that a lower cutoff temperature, e.g.,
85.degree. C., may inhibit formation of such "pops."
[0112] Additional components that may be used in conjunction with
interface module 110, temperature control subsystem 119, and power
control interface 290 of the present invention, e.g., a PIM 121 and
ICT 122 of catheter 120, are now briefly described with reference
to FIGS. 5A-6B.
[0113] In FIG. 5A, patient interface module (PIM) 121 that may be
associated with the integrated catheter tip (ICT) described further
below with respect to FIGS. 6A-6B is described. PIM 121 includes
interface module connector 501 that may be connected to front panel
111 of interface module 110, as described with reference to FIG.
1A; PIM circuitry 502, which will be described in greater detail
below with reference to FIG. 5B; ICT connector 503 that may be
connected to catheter 120; and PIM cable 504 that extends between
interface module connector 501 and PIM circuitry 502. PIM 121 is
preferably, but not necessarily, designed to remain outside the
sterile field during the ablation procedure, and optionally is
reusable with multiple ICT's.
[0114] FIG. 5B schematically illustrates internal components of PIM
circuitry 502, and includes first I/O port 505 configured to be
coupled to catheter 120, e.g., via ICT connector 503, and second
I/O port 506 configured to be coupled to interface module 110,
e.g., via PIM cable 504 and interface module connector 501.
[0115] PIM circuitry 502 receives on first I/O port 505 an analog
thermocouple (TC) signal, raw analog radiometer signals, and analog
ECG signals from catheter 120. PIM circuitry 502 includes TC signal
analog-to-digital (A/D) converter 540 that is configured to convert
the analog TC signal to a digital TC signal, and provide the
digital TC signal to interface module 110 via second I/O port 506.
PIM circuitry 502 includes a series of components configured to
convert the raw analog radiometer signals into a usable digital
form. For example, PIM circuitry may include radiometric signal
filter 510 configured to filter residual RF energy from the raw
analog radiometer signals; radiometric signal decoder 520
configured to decode the filtered signals into analog versions of
the Vref and Vrad signals mentioned above with reference to FIG.
3B; and radiometric signal A/D converter 530 configured to convert
the analog Vref, Vrad signals into digital Vref, Vrad signals and
to provide those digital signals to second I/O port for
transmission to interface module 110. PIM circuitry 502 also passes
through the ECG signals to second I/O port 506 for transmission to
interface module 110.
[0116] On second I/O port 506, PIM circuitry 502 receives RF
ablation energy from generator 130 (e.g., a Stockert EP-Shuttle or
70 RF Generator) via interface module 110. PIM circuitry 502 passes
that RF ablation energy through to catheter 120 via first I/O port
505. PIM circuitry 502 also receives on second I/O port 506 a clock
signal generated by RF circuitry within interface module 110, as
described further above with reference to FIG. 2B, and passes
through the clock signal to first I/O port 505 for use in
controlling microwave circuitry in ICT 122, as described below.
[0117] Referring now to FIGS. 6A-6B, an exemplary integrated
catheter tip (ICT) 122 for use with the interface module 110,
temperature control subsystem 119, and power control interface 290
of FIGS. 1A-2D and the PIM of FIGS. 5A-5B is described. Further
detail on components of ICT 122 may be found in U.S. Pat. No.
7,769,469 to Carr, the entire contents of which are incorporated
herein by reference, as well as in U.S. Patent Publication No.
2010/0076424, also to Can ("the Can publication"), the entire
contents of which are incorporated herein by reference. The device
described in the aforementioned patent and publication do not
include a thermocouple or ECG electrodes, which preferably are
included in ICT 122 configured for use with interface module
110.
[0118] As described in the Can publication and as depicted in FIGS.
6A-6B, ICT 122 includes an inner or center conductor 103 supported
by a conductive carrier or insert 104. Carrier 104 may be formed
from a cylindrical metal body having an axial passage 106 that
receives conductor 103. Upper and lower sectors of that body
extending inward from the ends may be milled away to expose passage
106 and conductor 103 therein and to form upper and lower
substantially parallel flats 108a and 108b. Flat 108a may include
coplanar rectangular areas 108aa spaced on opposite sides of
conductor 103 near the top thereof. Likewise, flat 108b may include
two coplanar rectangular areas 108bb spaced on opposite sides of
conductor 103 near the bottom thereof. Thus, carrier 104 may
include center segment 104a containing the flats and distal and
proximal end segments 104b and 104c, respectively, which remain
cylindrical, except that a vertical groove 107 may be formed in
proximal segment 104c.
[0119] Center conductor 103 may be fixed coaxially within passage
106 by means of an electrically insulating collar or bushing 109,
e.g. of PTFE, press fit into passage 106 at distal end segment 104b
of the carrier and by a weld to the passage wall or by an
electrically conductive collar or bushing (not shown) at the
carrier proximal segment 104c. This causes a short circuit between
conductor 103 and carrier 104 at the proximal end of the carrier,
while an open circuit may be present therebetween at the distal end
of the carrier. In the carrier center segment 104a, the walls 106a
of passage 106 may be spaced from center conductor 103. This forms
a quarter wave stub S, as described in greater detail in U.S. Pat.
No. 7,769,469 and U.S. Patent Publication No. 2010/0076424.
Conductor 103 includes distal end segment 103a which extends beyond
the distal end of carrier 104 a selected distance, and a proximal
end segment 103b which extends from the proximal end of ICT 122 and
connects to the center conductor of cable 105 configured to connect
to PIM 121.
[0120] As illustrated in FIG. 6B, mounted to the upper and lower
flats 108a and 108b of carrier 104 is a pair of opposed, parallel,
mirror-image, generally rectangular plates 115a and 115b. Each
plate 115a, 115b may include a thin, e.g. 0.005 in., substrate 116
formed of an electrically insulating material having a high
dielectric constant. Printed, plated or otherwise formed on the
opposing or facing surfaces of substrates 116 are axially centered,
lengthwise conductive strips 117, preferably 0.013-0.016 mm wide,
which extend the entire lengths of substrates 116. Also, the
opposite or away-facing surfaces of substrates 116 are plated with
conductive layers 118, e.g. of gold. The side edges of layers 118
wrap around the side edges of the substrates.
[0121] When the ICT is being assembled, plate 115a may be seated on
the upper flat 108a of carrier 104 and the lower plate 115b is
likewise seated on the lower flat 108b so that the center conductor
103 is contacted from above and below by the conductive strips 117
of the upper and lower plates and the layer 118 side edges of those
plates contact carrier segment 104a. A suitable conductive epoxy or
cement may be applied between those contacting surfaces to secure
the plates in place.
[0122] At least one of the plates, e.g. plate 115a, functions also
as a support surface for one or more monolithic integrated circuit
chips (MMICs), e.g. chips 122 and 124. The chip(s) may include a
coupling capacitor connected by a lead (not shown) to center
conductor 103 and the usual components of a radiometer such as a
Dicke switch, a noise source to provide a reference temperature,
amplifier stages, a band pass filter to establish the radiometer
bandwidth, additional gain stages if needed, a detector and buffer
amplifier. Due to the relatively small profile of the present ICT
122, the above circuit components may be arranged in a string of
four chips. The chip(s) may be secured to the metal layer 118 of
plate 115a by a suitable conductive adhesive so that that layer
which, as described above, is grounded to the insert 104 may
function as a ground plane for those chips. The plates also conduct
heat away from the chips to conductor 103 and carrier 104. Various
leads (not shown) connect the chips to each other and other leads
125b extend through carrier slot 107 and connect the last chip 124
in the string, i.e. the radiometer output, to corresponding
conductors of cable 105 leading to PIM 121.
[0123] A tubular outer conductor 126 may be slid onto carrier 104
from an end thereof so that it snugly engages around the carrier
with its proximal and distal ends coinciding with the corresponding
ends of the carrier (not shown). The conductor 126 may be fixed in
place by a conductive epoxy or cement applied around the carrier
segments 104b and 104c.
[0124] ICT 122 also may include an annular dielectric spacer 137,
e.g. of PTFE, which is centered on the distal end of carrier 104
and surrounds the conductor segment 103a. The spacer may have a
slit 137a enabling it to be engaged around that conductor segment
from the side thereof. The spacer 137 may be held in place by a
conductive collar 136 which encircles the spacer and is long enough
to slidably engage over a distal end segment of outer conductor
126. The collar 136 may be press fit around that conductor and
carrier segment 104b to hold it in place and to electrically
connect all those elements.
[0125] The distal end of the ICT 122 may be closed off by
conductive tip 142 which, in axial section, may be T shaped. That
is, the tip 142 may have discoid head 142a that forms the distal
end of the ICT and an axially extending tubular neck 142b. The
conductor segment 103a is sufficiently long to extend beyond the
distal end of the spacer 137 into the axial passage in neck 104b.
The tip may be secured in place by conductive adhesive applied
around the distal end of conductor segment 103a and at the distal
end or edge of collar 136. When the tip is in place, the conductor
segment 103a and tip 104 form a radiometric receiving antenna, as
described in greater detail in U.S. Pat. No. 7,769,469 and U.S.
Patent Publication No. 2010/0076424.
[0126] ICT 122 may further include dielectric sheath 144 which may
be engaged over the rear end of outer conductor 126 and slid
forwardly until its distal end 144a is spaced a selected distance
behind the distal end of tip 142. The conductors 103 and 126 of ICT
122 form an RF transmission line terminated by the tip 104. When
the ICT 122 is operative, the transmission line may radiate energy
for heating tissue only from the uninsulated segment of the probe
between tip 104 and the distal end 144a of the sheath 144. That
segment thus constitutes an RF ablation antenna.
[0127] The proximal ends of the center conductor segment 103b,
outer conductor 126 and sheath 144 may be connected, respectively,
to the inner and outer conductors and outer sheath of cable 105
that leads to PIM 121. Alternatively, those elements may be
extensions of the corresponding components of cable 105. In any
event, that cable 105 connects the center conductor 103 to the
output of a transmitter which transmits a RF heating signal at a
selected heating frequency, e.g. 500 GHz, to the RF ablation
antenna.
[0128] As illustrated in FIG. 6A, ICT 122 further may include
first, second, and third ECG electrodes 190 disposed on the outside
of sheath 144, as well as a thermocouple 191 positioned so as to
detect the temperature of blood or tissue in contact with ICT 122.
Signals generated by electrodes 190 and thermocouple 191 may be
provided along cable 105 connected to PIM 121.
[0129] If desired, cable 105 further may include probe steering
wire 145 whose leading end 145a may be secured to the wall of a
passage 146 in carrier segment 104c.
[0130] Preferably, helical through slot 147 is provided in collar
136 as shown in FIGS. 6A-6B. The collar material left between the
slot turns essentially forms helical wire 148 that bridges spacer
137. Wire 148 is found to improve the microwave antenna pattern of
the radiometric receiving antenna without materially degrading the
RF heating pattern of the RF ablation antenna.
[0131] The inner or center conductor 103 may be a solid wire, or
preferably is formed as a tube that enables conductor 103 to carry
an irrigation fluid or coolant to the interior of probe tip 142 for
distribution therefrom through radial passages 155 in tip head 142a
that communicate with the distal end of the axial passage in tip
neck 142b.
[0132] When plates 115a and 115b are seated on and secured to the
upper and lower flats 108a and 108b, respectively, of carrier 104,
conductive strips 117, 117 of those members may be electrically
connected to center conductor 103 at the top and bottom thereof so
that conductor 103 forms the center conducts for of a slab-type
transmission line whose ground plane includes layers 118, 118.
[0133] When ablation energy is provided to ICT 122, a microwave
field exists within the substrate 116 and is concentrated between
the center conductor 103 and layers 118, 118. Preferably, as noted
here, conductive epoxy is applied between conductor 103 and strips
117 to ensure that no air gaps exist there because such a gap would
have a significant effect on the impedance of the transmission line
as the highest field parts are closest to conductor 103.
[0134] Plates 115a, 115b and conductor 103 segment together with
carrier 104 form a quarter wave (.lamda..sub.R/4) stub S that may
be tuned to the frequency of radiometer circuit 124, e.g. 4 GHz.
The quarter wave stub S may be tuned to the center frequency of the
radiometer circuit along with components in chips 122, 124 to form
a low pass filter in the signal transmitting path to the RF
ablation antenna, while other components of the chips form a high
pass or band pass filter in the signal receiving path from the
antenna to the radiometer. The combination forms a passive diplexer
D which prevents the lower frequency transmitter signals on the
signal transmitting path from antenna T from reaching the
radiometer, while isolating the path to the transmitter from the
higher frequency signals on the signal receiving path from the
antenna.
[0135] The impedance of the quarter wave stub S depends upon the K
value and thickness t of substrates 116 of the two plates 115a,
115b and the spacing of center conductor 103 from the walls 106a,
106a of passage 106 in the carrier center segment 104a. Because the
center conductor 103 is not surrounded by a ceramic sleeve, those
walls can be moved closer to the center conductor, enabling
accurate tuning of the suspended substrate transmission line
impedance while minimizing the overall diameter of the ICT 122. As
noted above, the length of the stub S may also be reduced by making
substrate 116 of a dielectric material which has a relatively high
K value.
[0136] In one working embodiment of the ICT 122, which is only
about 0.43 in. long and about 0.08 in. in diameter, the components
of the ICT have the following dimensions:
TABLE-US-00002 Component Dimension (inches) Conductor 103 0.020
outer diameter 0.016 inner diameter (if hollow) Substrate 116 (K =
9.8) 0.065 wide; thickness t = 0.005 Strips 117 0.015 wide Air gap
between 103 and each 106a 0.015
[0137] Thus, the overall length and diameter of the ICT 122 may be
relatively small, which is a useful feature for devices configured
for percutaneous use.
[0138] While various illustrative embodiments of the invention are
described above, it will be apparent to one skilled in the art that
various changes and modifications may be made herein without
departing from the invention. For example, although the interface
module has primarily been described with reference for use with an
RF electrosurgical generator and the PIM and ICT illustrated in
FIGS. 5A-6B, it should be understood that the interface module
suitably may be adapted for use with other sources of ablation
energy and other types of radiometers. Moreover, the radiometer may
have components in the ICT and/or the PIM, and need not necessarily
be located entirely in the ICT. Furthermore, the functionality of
the radiometer, ICT, and/or PIM optionally maybe included in the
interface module. The appended claims are intended to cover all
such changes and modifications that fall within the true spirit and
scope of the invention.
* * * * *